In integrated circuit manufacturing, microelectronic devices such as capacitors are the basic energy storage devices in random access memory devices, such as dynamic random access memory (DRAM) devices, static random access memory (SRAM) devices, and ferroelectric memory (FERAM) devices. Capacitors typically consist of two conductors, such as parallel metal or polysilicon plates, which act as the electrodes (i.e., the storage node electrode and the cell plate capacitor electrode), insulated from each other by a layer of dielectric material.
The continuous shrinkage of microelectronic devices such as capacitors and gates over the years has led to a situation where the materials traditionally used in integrated circuit technology are approaching their performance limits. Silicon (i.e., doped polysilicon) has generally been the substrate of choice, and silicon dioxide (SiO2) has frequently been used as the dielectric material with silicon to construct microelectronic devices. However, when the SiO2 layer is thinned to 1 nanometer (nm) (i.e., a thickness of only 4 or 5 molecules), as is desired in the newest micro devices, the layer no longer effectively performs as an insulator due to the tunneling current running through it.
Thus, new high dielectric constant materials are needed to extend device performance. Such materials need to demonstrate high permittivity, barrier height to prevent tunneling, stability in direct contact with silicon, and good interface quality and film morphology. Furthermore, such materials must be compatible with the gate material, electrodes, semiconductor processing temperatures, and operating conditions.
High quality thin oxide films of metals, such as ZrO2, Ta2O5, HfO2, Al2O3, Nb2O5, and YSZ deposited on semiconductor wafers have recently gained interest for use in memories (e.g., dynamic random access memory (DRAM) devices, static random access memory (SRAM) devices, and ferroelectric memory (FERAM) devices). These materials have high dielectric constants and therefore are attractive as replacements in memories for SiO2 where very thin layers are required. These metal oxide layers are thermodynamically stable in the presence of silicon, minimizing silicon oxidation upon thermal annealing, and appear to be compatible with metal gate electrodes. Additionally, Nb2O5, Nb2O5 doped/laminated Al2O3, Ta2O5, and HfO2 films have been shown to be useful for capacitor and gate dielectrics. Nb2O5 doping/laminating has been shown to decrease leakage and stabilize crystalline phases.
Efforts have been made to investigate various deposition processes to form layers, especially dielectric layers, based on metal oxides. Such deposition processes have included vapor deposition, metal thermal oxidation, and high vacuum sputtering. Vapor deposition processes, which includes chemical vapor deposition (CVD) and atomic layer deposition (ALD), are very appealing as they provide for excellent control of dielectric uniformity and thickness on a substrate.